List widget: Ability to avoid empty entries

[papandreou]

(First off, I'm not sure if this is a duplicate of #467 or whether it will be addressed by the efforts to solve that. Feel free to just close it if that's the case -- would make me happy 😄)

Is your feature request related to a problem? Please describe.

When you have a list widget, it appears there's no way to validate that list entries aren't left blank. That means that if the user clicks the "Add XXX +" button and forgets to fill in the field, it will end up being persisted as either null or '' (depending on whether the field has been edited, probably due to #1449).

This is a problem for "non-technical" people that don't necessarily distinguish between the list entry being empty vs. not being there at all.

Here's an example setup where the problem can be reproduced:

backend:
  name: github
  repo: myrepo
collections:
  -
    name: foos
    label: Foos
    label_singular: Foo
    folder: foos
    create: true
    slug: "{{id}}"
    fields:
      -
        label: Id
        name: id
        widget: string
      -
        label: Title
        name: title
        widget: string
      -
        label: Bars
        label_singular: Bars
        name: bars
        widget: list
        allow_add: true
        field:
          name: id
          label: Bar
          required: true # <- this has no effect
          widget: string

Steps to reproduce:

1. Create a new Foo
2. Enter an id and a title
3. Click the "Add bars +" button
4. Click "Publish"

Causes something like this to be saved:

+---
id: the id
title: the title
bars:
  - null
---

Describe the solution you'd like
That required: true causes a validation error when publishing with list entry field is left without a value.

Describe alternatives you've considered
Alternatively unfilled list entries could simply be ignored when persisting.

Additional context

[igufi]

I came across the same issue when using list widget for setting post categories in Hugo. If a user writes anything to the category field and then deletes it, the post header will still contain the following:

categories: 
  - ''

This causes Hugo to create a post with an empty category tag, that can look something like this:

[lmcorreia]

I'm going to test a few possible edge cases such as the list itself having required: true but nested fields having required: false but at the very least the core problem presented here will be solved by the work done for #467

[erquhart]

@lmcorreia your comment on #2017 is also relevant here.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[erquhart]

Fixed by #467.